FR2733497A1 - PROCESS FOR THE PRODUCTION OF BUTENE-1 BY DIMERIZATION OF ETHYLENE COMPRISING AN IMPROVED RECOVERY AREA OF USED CATALYST - Google Patents

Abstract

The process for producing butene-1 comprises the following steps: a) introducing an inhibited catalyst containing a reaction effluent into an expansion zone in which the pressure is reduced from about 0.1 MPa to about 2 MPa, and the a first gas phase is obtained containing ethylene and butene-1, as well as a first liquid phase containing the inhibited catalyst; b) the first liquid phase resulting from step a) is passed through at least one vaporization zone allowing the separation of a second gaseous phase containing butene-1 and ethylene on the one hand and on the other hand. second liquid phase containing the inhibited catalyst on the other hand; c) the second liquid phase from step b) is then passed through at least one thin film evaporation section allowing the separation of a third gas phase containing ethylene, butene-1 and other heavier hydrocarbon products on the one hand and a concentrated inactivated catalytic solution on the other hand, and d) the first, second and third gaseous phases are collected to constitute a gaseous reaction effluent substantially free of spent catalyst.

Description

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  The present invention relates to an improved industrial process

  allowing the production of butene-1 from ethylene.

  There are numerous patents describing methods for synthesizing butene-1 by dimerization of ethylene. Among these, US-A-4,532,370 filed by the applicant describes a catalyst of very high activity and selectivity for butene-1. However, this process requires deactivation of the spent catalyst, which must then be separated from the reaction effluent by vaporization of almost all of the effluent. The catalyst separation zone requires specific vaporization equipment such as, for example, thin film evaporators for vaporizing the desired product. The present invention relates to an improved process for the production of butene-1 by dimerization of ethylene comprising an extremely efficient catalyst separation zone. The process of the invention, during which approximately 99% by weight of the reaction effluent is vaporized in two stages, first by means of an ordinary vaporizer and then of a thin film evaporator, has the advantage of limit the service of the thin film evaporator. This limitation considerably reduces the cost of installation. In addition, vaporization at elevated temperature and pressure often causes fouling of the vaporizer due to the modification of the properties of the polymers at elevated temperature in the vaporizer. High temperatures are avoided with the process of the invention, which effectively limits fouling of the vaporizer. Another very important advantage of the process according to the present invention results from the possibility of using one or more film evaporators

  thin, reduced size, which limits the cost of installation.

  Thus, the invention relates to an improved process for the production of butene-1 by homogeneous catalytic dimerization in the liquid phase of ethylene, at a pressure of 0.5 to 8 MPa and at a temperature of 20 C to 150 C, comprising a step during which a dimerization reaction effluent is brought into contact with a catalyst inhibitor, as well as a step for recovering a reaction effluent substantially free of catalyst and of a concentrated inactivated catalytic solution, said process being characterized in what it involves the following steps:

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  a) an inhibited catalyst containing a reaction effluent is introduced into an expansion zone in which the pressure is reduced from approximately 0.1 MPa to approximately 2 MPa and a first gas phase is obtained containing ethylene and butene-1 , as well as a first liquid phase containing the inhibited catalyst, b) the first liquid phase from step a) is passed through at least one vaporization section in which it is vaporized at a pressure substantially identical to that of l step a) and at a temperature allowing the separation of a second gas phase containing butene-1 and ethylene and a second liquid phase containing the inhibited catalyst, c) then passing the second liquid phase issuing of step b) in at least one thin film evaporation zone in which it is evaporated at a pressure substantially identical to that of step b), under conditions allowing the separation of a third e gas phase containing ethylene, butene-1, as well as other heavier hydrocarbon products, and a concentrated inactivated catalytic solution, and d) the first, second and third gas phases are collected to constitute a gaseous reaction effluent substantially free of spent catalyst. During the ethylene dimerization process, the reaction effluent always contains certain heavy components such as C6 (mainly olefinic compounds) and C6 + (mainly octene) formed during side reactions in the reactor. The catalyst remains dissolved in this

  heavy fraction and will be separated as a solution in this fraction.

  During the dimerization of ethylene, the reactor pressure preferably varies between 1.5 MPa and 3 MPa, the temperature preferably varies between C and 70 C and even more preferably between approximately 50 C and approximately 70 C. The reaction effluent is brought into contact with a sufficient quantity of catalyst inhibitor such as, for example, an oxygenated or nitrogenous polar compound intended to deactivate substantially all of the catalyst present in the effluent before passing this effluent through the relaxation area. Such nitrogen catalyst inhibitors are for example described in the patent.

European EP-B-200.654.

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  Within the expansion zone, the pressure of the reaction effluent will preferably be reduced from approximately 0.5 MPa to approximately 1 MPa. In this area, due to the drop in pressure, part of the effluent will be vaporized. The pressure drop is generally such that at least 5% by weight, for example 8% to 15%, of the effluent from the reactor is vaporized. The first liquid phase obtained is passed through the expansion zone into the vaporization zone which includes one or more vaporizers. In this vaporization zone, the temperature preferably varies between 60 C and 100 C and more preferably between 70 C and 90 C. Under these conditions, at least% by weight, for example 55% to 81%, of the reaction effluent are vaporized

in this area.

  The second liquid phase collected after the vaporization section is passed through a thin film evaporation zone which comprises at least one thin film evaporator and often two or more identical or even more thin film evaporators. In this zone, at most 25% by weight, for example 10% to 20

  % of the reaction effluent is generally vaporized.

  In a preferred embodiment, the gaseous reaction effluent substantially free of catalyst is condensed in the form of a liquid product which can be brought into a separation zone in which the butene-1 will be separated from the ethylene. The condensation is generally carried out at the pressure of the gaseous product collected at the end of each of the vaporization steps of the present invention. The liquid product obtained can then be compressed to a pressure substantially identical to the dimerization reaction pressure. This compression can be achieved by means of a centrifugal pump or any

other device known per se.

  The success of this new process depends on the concentration of ethylene in the reaction effluent and the possibility of transferring a maximum vaporization workload from the thin film evaporators to the vaporizer. It is obvious that the working pressure of the vaporizer plays an essential role in the transfer of the vaporization work. The process for obtaining butene-1 requires almost complete vaporization of the reaction effluent in order to separate the catalyst from the effluent, then complete condensation before the

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  distillation operations. A low operating pressure favors the vaporization of the reaction effluent in the vaporizer, while a high operating pressure promotes the recondensation of the reaction effluent in the feed condenser of the recycling column, in particular when the concentration ethylene is higher in the reaction effluent. This invention is based on the optimization of these vaporization and condensation pressures. According to this invention, a thin film evaporator is used to remove only a small amount of catalyst in solution. This avoids an unnecessary flow of liquid to the thin film evaporator. The mass of catalyst withdrawn from the bottom of the thin-film evaporator contains approximately 13% by weight per

  example of a non-vaporizable catalyst.

  i5 The refrigeration required for this new process is minimized by optimizing the flow of cooling water and chilled water, and by adapting the arrangement of the refrigerants for the circulating refluxes and the feed condensers of the recycling column. A minimum water cooling temperature is desirable to allow condensation of all of the vapors produced in the catalyst separation zone. The reactor containing butene-1 can be operated under conditions such that the concentration of ethylene in the reaction effluent varies between 10 and 15% by weight for example. With this low concentration of ethylene, the reaction effluent can be recondensed for example at 1.3 MPa and at 15 ° C. after separation of the catalyst. This recondensed liquid is then pressurized to the operating pressure chosen for the recycling column in order to separate ethylene from butene-1 and other heavy components. According to this invention, all of the vapors from the catalyst separation zone are preferably recondensed at a low pressure, for example at 1.3 MPa, since a pump is generally used to increase the pressure of the reaction effluent by passing it from a low value to the value of the pressure of the dimerization reaction, that is to say for example from 1.3 to 2.6 MPa. After fractionation, the unreacted ethylene is recycled to the reactor containing butene-1, the operating pressure of which amounts to approximately

2.3 MPa.

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EXAMPLES

  The examples presented below illustrate the invention without, however, limiting it.

the scope.

EXAMPLE 1

  This example presents in detail the material balance and the energy balance of a butene-1 production installation according to the invention. The example describes the material balance and the energy balance of 11.7 MT / h of butene-1 in the reaction effluent. The dimerization of ethylene is carried out at a temperature of 53 ° C. and at a pressure of 2.32 MPa in the presence of the catalyst described in example 1 of patent US-A-4,532,370 filed by the applicant. The pressure of the reaction effluent is lowered by 0.77 MPa (from 2.32 MPa to 1.55 MPa) by means of a pressure regulating valve which vaporizes approximately 10.1% by weight of the reaction effluent and decreases the temperature of the reaction effluent by 11 C (from 53 C to 42 C). 5 kg of decylamine, used as a catalyst inhibitor, are then added to the hot reaction effluent in order to deactivate the catalyst before the depressurization step. At the end of the depressurization step, the reaction effluent is sent to an expansion tank. The vapor stream formed in the upper part of the balloon is collected to be sent to at least one condenser. The contained liquid

  in the expansion ball is then transferred by pumping into a vaporizer.

  The liquid initially contained in the expansion tank is heated to 83 ° C. in the vaporizer. The pressure in the vaporizer being only 1.5 MPa, approximately 69.1% by weight of reaction effluent is vaporized at 83 C. This method makes it possible to pass 3 MT / h of liquid containing a small amount of catalyst in the thin film evaporation zone composed of two thin film evaporators arranged in series. 95% by weight of this liquid is vaporized in the first and in the second thin film evaporator and approximately 5% by weight constitutes the catalyst purge. The first, second and third streams from the flash tank, the vaporizer and the thin film evaporators respectively are then mixed to form a gas flow before being sent to two condensers arranged in series. All of the vapors are condensed at 1.31 MPa and 15 C. The limitation to

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   C of the condenser outlet temperature is imposed by the temperature

  cooled water (10 C). The material balance is presented in Table 1 below.

TABLE 1

EFFLUENT GAS FLOW PURGE

REACTIONAL CATALYST

  COMPONENT% WEIGHT COMPONENT% WEIGHT COMPONENT% WEIGHT

  methane 0.0338 methane 0.0 methane 0.0377 ethane 1.0709 ethane 0.0006 ethane 1.1019 ethylene 13.822 ethylene 0.0017 ethylene 14.135 butane-1 79.031 butene-1 13.342 butene-1 79.469 butane 0.0883 butane 0 , 0175 butane 0.0688 hexene- 1 5.5093 hexene- 1 59.401 hexene- 1 4.8649 hexane 0.3039 hexane 3.9689 hexane 0.2571 octane-1 0.1523 octene-1 7.5734 octane-1 0 .0615 catalyst inhibitor inhibitor inhibitor 0.0000 catalyst 2.4614 catalyst 0.0044 catalyst 0.1554 catalyst 13.234 catalyst 0.0

EXAMPLE 2

  In this example, the dimerization conditions are identical to those of Example 1, but the pressure in the catalyst separation zone is further reduced. The pressure in the catalyst separation zone is reduced from 0.1 MPa (1 bar) to 1.45 MPa, the liquid flow flowing to the thin-film evaporator goes from 3 to 2 MT / h, requiring thus an even smaller size thin film evaporator. The drop in pressure of one bar reduces the work provided by the thin film evaporator by 13%, which is however disadvantageous insofar as the condensation of approximately 274 kg of vapors at 1.21 MPa and 15 It's impossible. The total condensation of these vapors is nevertheless carried out at 1.21 MPa by reducing the temperature on the process side to 12 C at the outlet of the condenser.

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Claims (5)

  1) Process allowing the production of butene-1 by homogeneous catalytic dimerization in ethylene liquid phase at a pressure varying between 0.5 MPa and 8 MPa and at a temperature varying between 20 C and 150 C, comprising a step during which a dimerization reaction effluent is brought into contact with a catalyst inhibitor and a step for recovering a reaction effluent substantially free from catalyst and from a concentrated inactivated catalytic solution, characterized in that said process comprises the following steps: a ) an inhibited catalyst containing a reaction effluent is introduced into an expansion zone in which the pressure is reduced from approximately 0.1 MPa to approximately 2 MPa, and a first gas phase is obtained containing ethylene and butene-1 , as well as a first liquid phase containing the inhibited catalyst, b) the first liquid phase from step a) is passed through at least one vapor zone oration in which it is vaporized at a pressure substantially identical to that of step a) and at a temperature allowing the separation of a second gas phase containing butene-1 and ethylene and a second liquid phase containing the inhibited catalyst, c) the second liquid phase from step b) is passed through at least one thin film evaporation zone in which it is evaporated at a pressure substantially identical to that of step b), under conditions allowing the separation of a third gas phase containing ethylene, butene-1 and other heavier hydrocarbon products and a concentrated inactivated catalytic solution, and d) the first, the second and the third gas phase to constitute a gaseous reaction effluent substantially free of catalyst. 2) Method according to claim 1, characterized in that said gaseous reaction effluent substantially free of catalyst is condensed under the form of a liquid product. 8 2733497   3) Method according to claim 2, characterized in that the liquid product is brought into a separation zone in which the butane-1 is separated from the ethylene. 4) Process according to claim 1, characterized in that the dimerization of ethylene is carried out at a pressure varying between 1.5 MPa and 3 MPa and at   a temperature varying between 30 C and 70 C.   ) Method according to claim 4, characterized in that the pressure in the   expansion tank is reduced from approximately 0.5 MPa to approximately 1 MPa.   6) Method according to claim 5, characterized in that the temperature in the   vaporization area varies between around 60 C and 100 C.   7) Method according to claim 6, characterized in that the evaporation zone   thin film has only one thin film evaporator.   8) Method according to claim 6, characterized in that the thin film evaporation zone comprises at least two thin film evaporators connected in series.